1. Field of the Invention
The present invention relates to electronics and, in particular, to amplifier systems and interface units for cell sites for wireless communications systems.
2. Description of the Related Art
It is desirable, in certain circumstances, to upgrade a cell site in an existing wireless communications system conforming to the Global System for Mobile communications (GSM) standard to support communications conforming to other wireless communications standards, such as the Universal Mobile Telecommunications System (UMTS) standard, while continuing to support communications conforming to the GSM standard. In addition, it may be desirable to do so in a manner that does not increase the number of antennas in the cell site. It may also be desirable to do so in a manner that does not significantly degrade the transmitted power of the GSM downlink signals or the receiver sensitivity to the GSM uplink signals.
For example, a conventional GSM-only cell site may be configured with two antennas and a GSM base station having two GSM transceivers, where each base station transceiver is connected to a different antenna for both downlink and uplink signal processing and the diversity receive signal is derived from the other antenna inside the GSM base station. A UMTS base station can be added to such a cell site to upgrade the cell site to support both GSM and UMTS communications. One issue is how to handle the different GSM and UMTS downlink and uplink signals without increasing the number of antennas.